Copper quadrupole coupling constants in binary mixtures of acetonitrile with some other nitriles at 298 K

Abstract

63Cu and 65Cu nuclear magnetic resonance (NMR) and viscosity studies of 0.064 M CuClO 4 have been made in binary mixtures of acetonitrile (AN) with succinonitrile (SN), adiponitrile (ADN), n-butyronitrile (n-BTN) and iso-butyronitrile (iso-BTN) as co-solvents at 298 K using 500 MHz NMR spectrometer and an Ubbelohde viscometer, respectively. Chemical shift ( δ) and linewidth (Δ) for both 63Cu and 65Cu signals have been recorded relative to 0.064 M CuClO 4 solution in pure anhydrous AN. Quadrupole relaxation rates (1/ T 2) Q , reorientational correlation times ( τ R) and copper quadrupole coupling constants ( e 2 Qq/h) have been calculated in all cases. The variation of these NMR parameters has been examined as a function of molecular percent co-solvent to compare the relative effects of these co-solvents on the solvation behaviour of Cu + and hence on the stabilization of copper (I) complexes formed. The ( e 2 Qq/h) values in all AN+nitrile mixtures are larger than the values in pure AN and increase with the increase of molecular percent co-solvent. The strong increase of ( e 2 Qq/h) values in all AN+nitrile mixtures with the increase of molecular percent co-solvent indicates the formation of mixed complexes of the form [Cu(CH 3CN) 4− x (S) x ] + ( x=1−4) due to the replacement of AN molecules from the original complex [Cu(CH 3CN) 4] + formed in pure AN by the co-solvent molecules (S). The results also show that mixed copper (I) complexes in all cases remain stable even at high co-solvent compositions. The ( e 2 Qq/h) values also indicate that the effect of dinitriles is relatively stronger than that of mononitriles, the effect of 63Cu isotope is relatively stronger than that of 65Cu and the effect of iso-BTN is relatively stronger than that of n-BTN in the formation of mixed copper (I) complexes.